A new polytype of orthoboric acid, H3BO3-3T

Shuvalov, Robert R.; Burns, Peter C.

doi:10.1107/s0108270103009685

Cited by 35 publications

(26 citation statements)

References 13 publications

(5 reference statements)

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“…[10] Compactness and the relative energies of the conformers of 4 and CA C H T U N G T R E N N U N G (OMe) 4 : The calculated minimum energy structures of these molecules have S 4 symmetry but each also has a slightly higher energy conformation with D 2d geometry ( Table 5). Figure 4 shows the structures of each conformation.…”

Section: Moleculesmentioning

confidence: 99%

Ligand Close Packing, Molecular Compactness, the Methyl Tilt, Molecular Conformations, and a New Model for the Anomeric Effect

Gillespie

Robinson

Pilmé

2010

Chemistry A European J

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All the atoms in a molecule attract each other until they reach their equilibrium positions at which point the repulsive forces between the atoms just balance the attractive forces and there are no resultant forces acting on any of the atoms in the molecule. Thus, we can consider that in the equilibrium geometry the atoms in a molecule are arranged as compactly as possible. This is the basis of the ligand close packing (LCP) model according to which three or four monatomic ligands X, such as F, Cl or O (formally =O or O(-)) pack as closely as possible around a small central atom such as a boron or carbon atom giving a truly close-packed equilateral triangular AX(3) molecule or a tetrahedral AX(4) molecules. Such monatomic ligands can, to a good approximation, be described as having a spherical shape with a single ligand radius r(X). In contrast, ligands with donor atoms with lone pairs such as the oxygen atom in an OX group have a less symmetrical electron density requiring two ligand radii, r(O(lp)) in the lone pair direction, and r(O(b)) in the bonding direction, where r(O(lp)) < r(O(b)) for an approximate description. On this basis we propose an explanation for the "methyl tilt", in methanol and many related molecules, and in conjunction with the concept of compactness, a model for explaining the relative energies of the conformations of molecules containing OH and OMe ligands, including molecules that exhibit the anomeric effect. We compare our model for the anomeric effect with the widely accepted "hyperconjugation" model. We also discuss the relationship between the concept of compactness and the concept of hardness.

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Section: Moleculesmentioning

confidence: 99%

Ligand Close Packing, Molecular Compactness, the Methyl Tilt, Molecular Conformations, and a New Model for the Anomeric Effect

Gillespie

Robinson

Pilmé

2010

Chemistry A European J

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“…12 However, the stacking sequences of the sheets differ between the two polymorphs, with ABCABC stacking in H 3 BO 3 -3T (space group P3 2 ), while ABAB in H 3 BO 3 -2A (space group P 1). 15 The crystal structure of 2,4,6-triethynyl-1,3,5-triazine (TET), reported by Ohkita et al, is a unique two-dimensional hexagonal network (Fig. 4).…”

Section: Soumyajit Ghoshmentioning

confidence: 99%

Mechanical properties of molecular crystals—applications to crystal engineering

2010

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Image reproduced with permission from Abbie TrewinOther articles published in this issue include:Dipyrrin based homo-and hetero-metallic infinite architectures Stéphane A. Baudron, CrystEngComm, 2010,We present an overview of very recent advances in the understanding of structure-mechanical property correlations in molecular crystals. After the introductory part on some classical twodimensional structures from the literature, we survey recent reports (mostly since 2005) pertinent to the mechanical properties of molecular crystals studied by application of external stress using a range of techniques. This includes both qualitative (shearing, bending and brittle crystals) and quantitative (nanoindentation, powder compaction and high-pressure) studies on establishing the correlation of anisotropic mechanical behaviour with the underlying crystal structure. Section 9, emphasizes on the usefulness of crystal engineering approach to improve the mechanical properties of molecular crystals, particularly the active pharmaceutical ingredients for their better tabletability properties. The parallels of the phenomena in other class of well studied materials are also appropriately drawn and discussed in the context of structure-mechanical property relationship. In the final part we comment on the prospects and ramifications of this emerging field.

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“…Each sheet is formed by H 3 BO 3 molecular units with nearly perfect C 3 h symmetry, linked together through hydrogen bonds. Later, the exploratory research on boron synthetic compounds by Shuvalov and Burns indicated the crystallographic structure of a new trigonal polytype of boric acid, H 3 BO 3 - 3T , with triple-layer sheets stacked in the repeating sequence pattern ABC .... Therefore, the two crystalline layered boric acid polymorphs were labeled as H 3 BO 3 - 2A (double layer) and H 3 BO 3 - 3T (triple layer).…”

Section: Introductionmentioning

confidence: 99%

Vibrational Properties of Bulk Boric Acid 2A and 3T Polymorphs and Their Two-Dimensional Layers: Measurements and Density Functional Theory Calculations

et al. 2018

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Boric acid (HBO) is being used effectively nowadays in traps/baits for the management of Aedes aegypti L. and Aedes albopictus Skuse species of mosquitoes, which are the main spreading vectors worldwide for diseases such as malaria, dengue, and zika. Previously, we published results on the structural, electronic, and optical properties of its molecular triclinic HBO-2A and trigonal HBO-3T polymorphs within the framework of density functional theory (DFT). Because of the renewed importance of these materials, the focus of this work is on the vibrational properties of the bulk boric acid 2A and 3T polymorphs. We measured the infrared and Raman spectra of the former, which was accompanied and interpreted through state-of-the-art DFT calculations, supplemented by computations regarding the HBO molecule and two-dimensional layers based on the bulk structures. We identify/assign their normal modes and find vibrational signatures for each polymorph as well as in- and out-of-plane motions and molecular vibrations, unveiling a nice agreement between the DFT level of theory employed and our improved spectroscopic measurements in the wavenumber ranges of 400-2000 cm (infrared) and 0-1500 cm (Raman). We show that a dispersion-corrected DFT functional within the generalized gradient approximation (GGA) can be very accurate in describing the vibrational properties of the boric acid polymorphs. Besides, several issues left open/not clearly resolved in previously published works on the vibrational mode assignments of the bulk and 2D sheets of boric acid are explained satisfactorily. Finally, phonon dispersions and associated densities of states were also evaluated for each polymorph along with their temperature-dependent DFT-calculated entropy, enthalpy, free energy, heat capacity, and Debye temperature. In particular, our DFT calculations suggest a possible way to differentiate the 2A and 3T boric acid polymorphs through Raman spectroscopy and heat capacity measurements.

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A new polytype of orthoboric acid, H₃BO₃-3T

Cited by 35 publications

References 13 publications

Ligand Close Packing, Molecular Compactness, the Methyl Tilt, Molecular Conformations, and a New Model for the Anomeric Effect

Ligand Close Packing, Molecular Compactness, the Methyl Tilt, Molecular Conformations, and a New Model for the Anomeric Effect

Mechanical properties of molecular crystals—applications to crystal engineering

Vibrational Properties of Bulk Boric Acid 2A and 3T Polymorphs and Their Two-Dimensional Layers: Measurements and Density Functional Theory Calculations

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